allowable bending stress 1

[par060]

I am reinforcing a curtain wall with a piece of plate steel .5in x 5 in. I attached the reinforcing to the mullion wall with screws to pick up the horizontal shear so I now have a transformed section. I found the stress in the steel to be 4 ksi....now I am unsure what to check this against....I want to say .6 Fy but I can't back that up with anything....if someone could help me out I would be much obliged. Thanks

 

[JAE]

If it is in tension, you could probably justify 0.6 Fy x 1.33 for the allowable stress. With wind working both ways, you would also have compression as well.

For the compression, I would check my plate against local buckling (compact vs. non-compact) per AISC ASD Table B5.1. Then, for the "global" mullion "beam" I would look at lateral torsional buckling. Are their horizontal elements that can brace the built-up mullion against lateral twist or translational movement of your plate? What is then, the unbraced length of your composite section and treat it as a beam under moment with unbraced length L.

Also...have you checked the material of the mullion against compression? It may be a weaker material and actually control your design vs. the steel plate.